Breeding improved tomato varieties involves providing genetics that give an advantage to the grower, processor, consumer, or other member of the supply chain. The improvement may be in the form of field performance, disease resistance, factory performance, or a fruit quality characteristic. For a tomato variety to be suitable to be grown for processing, the variety must have a concentrated fruit setting and maturity, firm fruit, and sufficient rot tolerance to allow early fruit to remain rot-free while later fruit continues to develop and ripen.
Most commercial processing tomato varieties are hybrids resulting from a cross pollination of two true-breeding, inbred parents. Through the use of true-breeding lines, a hybrid is produced that often displays characteristics of each parent, and often demonstrates characteristics that are superior to either parent alone, or that allow a hybrid to mask inadequacies of the individual parents.
Processing tomato varieties combining high levels of tolerance to bacterial canker (Clavibacter michiganense ssp. michiganense), early blight (Alternaria solani), and bacterial spot (Xanthomonas spp.) are highly desirable in humid climates where these diseases present production issues.
Moreover, tomato varieties adapted to arid climates, combining resistance to tomato spotted wilt virus (TSWV) and race 3 of Fusarium oxysporum f. sp. lycopersici, are desirable to the processing industry in California and other global tomato processing regions where these disease limit production. Additionally, tomato varieties adapted to arid climates that combine resistance to TSWV with high levels of soluble solids (° Brix), thin viscosity, and strong yields are also highly desirable for the California processing industry.
Further, Fusarium oxysporum f. sp. lycopersici race 3 (Fusarium 3) is a growing problem in the California tomato growing region and in other production areas worldwide, such as the Dominican Republic and Mexico. Productive, adapted varieties have been in demand by growers and processors since the mid 1990's with resistance to this pathogen. The disease has become a major limiting factor in tomato production in some California fields. Growers and processors need a range of tomato varieties with Fusarium 3 resistance, since products specifications vary in regards to juice viscosity, soluble solids content, field storage, and general field adaptability.
An additional important contribution that tomatoes provide to the human diet is the antioxidant lycopene. Specifically, processing tomato varieties are the key form of tomato intake in the US diet. Higher levels of lycopene are beneficial both from a nutritional standpoint and from a consumer perception and quality standpoint. Tomato varieties having higher levels of lycopene result in products with a deeper red color that can be considered an indicator of higher product quality. Thus, a tomato variety with higher levels of lycopene can be valuable from both a nutritional standpoint and a quality standpoint. However, to be commercially viable and useful, the tomato variety must perform acceptably as required by any other processing tomato variety. Previous varieties with increased lycopene levels have shown severe reductions in fruit quality, firmness, yield, and a sensitivity to fruit rots.